1. Field of the Invention
The present invention relates to a sleeve for an optical connector which is arranged between an optical fiber and an optical element module and serves to transmit light emitted from one to the other. The present invention also relates to a receptacle constituting an optical connector together with an optical plug and provided with the sleeve for the optical connector.
2. Description of the Related Art
A typical sleeve for an optical connector (hereinafter referred to as xe2x80x9csleevexe2x80x9d) located between the optical fiber and the optical element module is disclosed in J-UM-6-33443 by the inventors of the invention.
FIG. 12 is a horizontal sectional view of a conventional optical connector, and FIG. 13 is a horizontal sectional view of the receptacle shown in FIG. 12. In FIGS. 12 and 13, reference numeral 1 denotes a sleeve, and reference numeral 2 denotes an optical connector.
Sleeves 1 are attached to a receptacle (connector on the side of a device) constituting the optical connector 2. These sleeves 1 are arranged between optical element modules 4 (consisting of a light receiving element module and a light emitting element module) and a pair of optical fibers 6 which are attached to an optical plug (connector on the side of the optical fiber) constituting the optical connector 2, respectively. The sleeves 1 serve to make an optical connection between the optical element modules 4 and optical fibers 6.
A more detailed explanation will be given of the optical connector 2 as well as the sleeves 1.
The optical connector 2 includes the receptacle 3 and the optical plug 5 fit into the receptacle 3.
The receptacle 3, as shown in FIGS. 12 and 13, has a housing 7 made of synthetic resin and having a pair of housing chambers 8. The housing chambers 8 each houses an optical element module 4 which is supported by a back sheet 9 made of elastic material such as rubber. The rear of the housing chambers 8 is covered with a cap 10. The receptacle 3 has a pair of receiving cylinders 12 which are arranged in front of the housing chambers 8, and extended forward so as to accord with the respective axes of lenses 11. The sleeves 1 are inserted in the receiving cylinders 12, respectively.
The sleeve 1 can be formed by grinding both end surfaces of the optical fiber composed of a core and a cladding (not shown) after it has been secured to a cylindrical holder 14.
On the other hand, the optical plug 5 fit in the receptacle 3, as seen from FIG. 12 and 14 which is a horizontal sectional view of the optical plug shown in FIG. 12, includes a pair of ferule assemblies 15 each covering the optical fiber with its end face exposed at the tip of the assembly, a plug housing 17 with a pair of cylindrical partitions 16 for protecting the ferule assemblies 15 housed therein, a spring cap 17 fit over the plug housing 18 and a boot 19 fit over the rear of the spring cap 18.
The plug housing 17 has shoulders 17a each to be engaged with a flange 15a formed on the rear half of the periphery of each ferule assembly 15. The ferule 15 is urged forward normally by a spring 20 which is located between the flange 15a and inner cylinder 18a of the spring cap 18.
As shown in FIG. 14, by engagement between the flange 15a and shoulder 17a, the tip A of the ferule assembly is always pulled more internally than the tip of the plug housing 17. The tip A of the ferule assembly 15 corresponds to the light-incident/emitting face of the optical fiber 6.
As regards the above configuration, referring to FIG. 12, an explanation will be given of connection between the receptacle 3 and the optical plug 5.
When the receptacle 3 is fit over the optical plug 5, the receiving cylinders 12 advance into the plug housing 17, and the ferule assemblies 15 also advance into the receiving cylinders 12. At this time, the ferule assembly 15 is brought into contact with the tip of the receiving cylinder 12 and a suitable contact pressure is kept by the elastic force by the spring 20.
In this state, the tip A (FIG. 14) and sleeve 1 are arranged with a minimum gap (not shown) kept. Therefore, the loss of the gap can be minimized.
The prior art described above, in which the sleeve 1 has an optical fiber 13 and is formed in a ring-shape, presents the following problems.
As shown in FIG. 15, with respect to a light beam c1 (within a range of a critical angle) which is propagated through an optical fiber 6 and sleeve 1 along an optical path indicated by arrow in FIG. 15, when the light receiving face 4a of the light receiving element module 4 is smaller than the light-emitting face 1a of the sleeve 1 (the width of the module 4 is smaller by d than that of the optical fiber 13 on the one side with respect to a center line), the light beam c1 may not be received by the light receiving element module 4. This is one of causes reducing the transmission efficiency.
Although not shown, when the light beam emitted from the light emitting face (not shown) of the light emitting element module is diffusive-LED light, part of the light cannot enter the sleeve 1. This is one cause reducing the transmission efficiency. Even if such a light beam is incident on the sleeve 1, it becomes a light beam c2 out of the critical angle range. Therefore, the light c2 does not reflect totally but permeates through the sleevel. The light c2 will be not be propagated.
Further, the prior art intends to minimize the gap loss to improve the transmission efficiency. However, a slight gap between the optical fiber 6 and sleeve 1 and axis displacement therebetween may influence the transmission efficiency.
There is also a problem relative to productivity of the sleeve 1 as well as the problem of the transmission efficiency.
Specifically, as described above, in order to improve the optical characteristic (transmission efficiency of light) of the sleeve 1, after the optical fiber 13 is inserted in and attached to the holder 14, both end surfaces of the optical fiber 13 as well as the holder 14 must be ground using abrasives of plural grain sizes. Thus, production of the sleeve 1 requires many manufacturing steps inclusive of necessary previous steps of making its components, and is inferior in productivity.
Further, production of the sleeve 1, which requires monitoring the production status of its components and testing the size, is involved with complicate production management. This deteriorates the productivity of the sleeve and increases the production cost.
It is also demanded to assemble the sleeve with a receptacle smoothly.
A first object of the invention is to provide a sleeve for an optical connector, capable of improving the transmission efficiency and improving the productivity to reduce the production cost.
A second object of the invention is to provide an improved receptacle which can be smoothly assembled with the sleeve.
In order to attain the first object, in accordance with the invention, there is provided a sleeve comprising: a core of transparent synthetic resin; and a cladding of transparent synthetic resin and having a smaller refractive index than the core, wherein the core includes an optical waveguide extending in an optical axial direction with an outer wall to taper in a conical shape and a lens formed at the large diameter end of the waveguide, the lens receiving light and converging it, and the cladding is formed concentrically with the core in intimate contact with an side wall of the core.
In this configuration, the light outgoing from one of the optical fiber and optical element module is received and converged by the lens. The light is propagated through the waveguide while repeating total reflection and gradually converged. Thus, the transmission efficiency of light is improved.
The discrepancy of the optical axis from the sleeve can be relaxed by the lens. The outer wall of the waveguide is covered with the cladding which prevents scratch or dust from being deposited. This contributes to an improvement of transmission efficiency of light and also to easiness of the work of assembling. Further, the sleeve is made in such a manner that the cladding is formed in contact with the outer wall of the waveguide after the core is molded. Therefore, if the molding die for the core is mirror-finished, polishing is not required afterwards. The high accuracy of dimension of the molding die permits the suitable supply of the sleeve for the optical connector. Thus, the sleeve can be made by a fewer steps than the prior art.
Preferably, the core has a circular flange-like guide integral to the outer wall in the vicinity of the lens, the guide having a belt-shaped circumferential surface to be coplanar with that of the cladding. In this configuration, the guide and cladding serve as the holder in the conventional sleeve. This reduces the number of components by one. Further, provision of the guide easily assures the gate position of the core. The cladding can be molded while the guide is held.
Preferably, the guide has an end face flush with an apex of the lens. In this configuration, when either one of the optical fiber and the optical element module is brought into contact with the end face of the guide, the apex of the lens is also brought into contact therewith. Therefore, gap loss between the apex and lens can be restricted. The lens is also protected by the guide.
Preferably, the cladding and/or the guide has a groove or projection formed on their outer surface. In this configuration, the sleeve can be assembled into the receptacle without misconceiving the direction of assembling.
Preferably, the sleeve has an open space formed at a small diameter end of the waveguide so as to separate the core from the cladding. In this configuration, a part of the molding die can be arranged in the open space when the cladding is molded. This permits the core to be surely held within the molding die when the cladding is molded, thus increasing the productivity.
The cladding is made distinguishable from the core and colored so as to reflect light propagated through the waveguide.
In this configuration, the sleeve can be assembled into the receptacle without misconceiving the direction of assembling.
Preferably, the lens is covered with an antireflective coating. Therefore, it is possible to prevent the amount of light incident on the lens from reduced. Thus, a large amount of light can be incident on the lens and propagated.
Preferably, the sleeve comprises a light emitting element embedded in the waveguide.
The sleeve and the one-core type fiber bi-directional communication system can further provide the effects of miniaturization, cost reduction and improvement in reliability.
In accordance with the invention, there is provided a receptacle including the sleeve and optical element modules having a light emitting element and a light receiving element module, wherein the sleeve is located between each of the optical element modules and corresponding one of two fibers of an optical plug coupled with the receptacle. In this receptacle, the transmission efficiency of light is improved and work relative to assembling is simple.
The above and other objects and features of the invention will be more apparent from the following description taken in conjunction with the accompanying drawings.